1. Field of the Invention
The present invention relates in general to a recording apparatus. In particular, the invention relates to an ink jet recording apparatus having a printing head to record a desired image on a recording medium, a driver element for driving the printing head, and a flexible wiring board for transmitting signals from the driver element to the printing head.
2. Discussion of Related Art
There is conventionally known an ink-jet recording apparatus for recording a desired image on a recording medium such as a sheet of paper, which apparatus is adapted to eject, onto the recording medium, a droplet of ink through a plurality of nozzles formed in a printing head so that the desired image is formed on the recording medium. On the ink-jet recording apparatus, there is mounted an ink carriage which is reciprocable in a direction along a printing area of the printing medium. A head holder is mounted on the ink carriage. The printing head, a circuit board for supplying drive signals to the printing head, and a flexible wiring board for connecting the printing head and the circuit board are disposed on the head holder. Such an ink-jet recording apparatus is disclosed in U.S. Pat. No. 6,305,784, for example.
Due to the existing tendency that the number of the nozzles increases and density thereof also increases, wiring between a driver IC chip as the driver element generating drive signals and a printing head becomes thinner and denser, making the drive signals on the wiring susceptible to noise. Further, the number of interconnections between wires of the circuit board and wires of the flexible wiring board increases. There is disclosed, in U.S. patent application No. 2002-0105567, an arrangement for dealing with the above-described drawbacks, where driver IC chips are mounted on respective flexible wiring boards to have each driver IC chip as close as possible to the corresponding printing head.
With the increase in the number of nozzles, heat generated by the driver IC chips increases. To release this heat, the driver IC chips are pressed by an elastic member such as a sponge member, onto a cover plate which covers the flexible wiring board, so that the cover plate serves as a heatsink. The above-mentioned U.S. patent application No. 2002-0105567 discloses this arrangement, too.
On the other hand, there is a request to further increase the number of the nozzles. However, such an increase leads to a larger amount of heat generated at the driver IC chips, and accordingly requires enlarging the heatsink. In addition, a condenser preventing an excessive voltage drop and a connector connecting a control portion in a main body of a printer including the recording apparatus and the circuit board, which are essentially disposed on the circuit board, must be enlarged if the number of nozzles increases. Since the circuit board is positioned adjacent to the flexible wiring board, the increasing the sizes of the heatsink, condenser and connector leads to mutual intervention of the three members. Further, in a case where the head holder has a small size, the size of the heatsink is limited and therefore the heat generated at the driver IC chips can not be effectively released. In this case, performance of the driver IC chips may be deteriorated, or the driver IC chips may be damaged.
Furthermore, according to the recording apparatus disclosed in the U.S. Patent Application indicated above, a foreign material may be introduced between the heatsink and one of the driver IC chips during an assembly process of the apparatus. If such introduction of a foreign material occurs, the driver IC chip may be damaged, since the driver IC chip is pressed onto the heatsink by the elastic member and subjected to a local pressure due to the presence of the foreign material. In addition, the foreign material introduced between the heatsink and the driver IC chip deteriorates close contact between the heatsink and the driver IC chip, lowering heat conduction from the driver IC chip to the heatsink. Further, since a surface of the driver IC chip functions as a ground electrode, when an electrical noise which deteriorates print quality occurs at one of the driver IC chips, the noise is propagated to other driver IC chips through the heatsink.